In 1889 Mr. Holway found in Iowa, a physarum of which he sent part to Ellis and the remainder to the writer who, then engaged on the _Myxomycetes of East. Iowa_, referred his part of this Iowa gathering to the _Physarum auriscalpium_ Cke. as found in New York. Under this caption a specimen was later sent to Mr. Lister, who has, as we see, consistently regarded the thing as a variety of _P. virescens_ Ditmar, _P. nitens_ List. Meantime in 1898 Colorado material from Professor Bethel reached the University. This did not recall any of the materials sent from Ellis. _Diderma albescens_ had meanwhile come again from California, and been recognized as _Diderma niveum_ Rost. Accordingly, in _N. A. S._ the latest arrival from Colorado was described as a new species, and with some temerity perhaps, offered as a second species of the hitherto monotypic _Leocarpus_, all on account of the peculiar capillitium. Sometime after publication our most valued correspondent Mr. Bilgram called attention to the resemblance between the Colorado and Louisiana material already referred to. The University specimens as stated were small, broken, and in every way poor, but enough remained to indicate the evident justice of our correspondent's suspicion. Further investigation of the Holway material in Philadelphia showed that _it too was entitled to consideration_! Inasmuch as the Holway sending was all from one plasmodium, all difficulties vanished at once. The Iowa gathering showed two phases: one at the University represents _P. nitens_, physaroid, single-walled; while the Philadelphia part of the gathering corresponds, poorly it is true, but in fact, as _now_ appears, to the form coming in perfection from Colorado; leocarpine in structure, published as _Leocarpus fulvus_; _P. fulvum_ Lister. Since the combination _P. fulvum_ is already in use, synonym of _P. rubiginosum_, it seems better to write the name suggested by Ellis; _Physarum albescens_ never having been published, because _Diderma albescens_, as noted took care of itself. Since Rostafinski we separate all these physaroid forms chiefly by capillitial characters: capillitial structure separates genera. _Physarum diderma_ is a physarum despite its double wall. And so here _Leocarpus_ was set out by its differentiating capillitium. In good specimens of the present species a large part of the capillitial net is entirely free from lime, so that when the peridium first opens at the summit, sometimes no trace of lime appears; the calcareous deposits are below, and tend to occupy not the nodal intersections as in _Physarum_, but in large masses involve portions of the net itself, nodes and all, as in _Leocarpus_. Miss Lister's beautiful figures, _op. cit._, Figs. 66 and 82, show this very well.